I hope you are not thinking they would be using both spinnaker and screacher at the same time. They just carried both on the deck and used whichever one seemed most appropriate for the conditions.
Right, seeing how they had this rigged would be interesting. There are severaly ways I can think of doing it, but learning from their experiences would be good. Not many beachcats have gone that route, so it is a very good thing to have documented.